I'm not in the mood to preface this post. To quote Homestar Runner, "I'm not very good at speeches..."
Here is the rating system I'm using for this show:
★✯✯✯✯ - pretty bad
★★✯✯✯ - not so good
★★★✯✯ - pretty average
★★★★✯ - good
★★★★★ - pretty great
'Conquest Of Cuteness'
Finn and Jake get attacked by an army of cute little fluffy guys who want to conquer them. They pose no real threat, but Finn and Jake feel bad for them, because they've clearly never won a battle before. Not a great way to start off the season, but the final battle scene helps make this an entertaining episode nonetheless. It's fun and easy to watch.
'Morituri Te Salutamus'
Finn and Jake enter a cursed arena that pits them against the souls of fallen warriors. Finn starts to act crazy and Jake distracts himself with tropical island music. I love the self-awareness of this episode, as it basically lays out the entire plot within the first minute or two, and does so in a hilarious way. It's simple, to the point, and lots of fun.
'Memory Of A Memory'
Marceline passes out in her house and Finn and Jake are taken to her to find a way inside her mind to reverse the sleep spell she accidentally cast on herself. I don't want to give away much more away about the plot that this, but suffice it to say this is a very intelligently constructed and entertaining episode. Definitely one of Marceline's better episodes (at the time, at least).
Finn grounds the Ice King, who gets mad and hires someone to hit Finn and Jake. But he doesn't realize what a Hitman is, which leads to several assassination attempts. It's such a ridiculous and over the top silly episode, but that's what makes it someone funny. Ice King is so childish and innocent here, and his attempts at thwarting the hitman he hired himself are often pretty great.
Following the de-ageing events of season 2's finale, Princess Bubblegum loses her title to Earl of Lemongrab for being too young to hold the throne. Finn and PB try to prank her way back into power. Lemongrab is one of my favorite villains in the show, and his first appearance sets the tone for him perfectly. It's a light-hearted episode and features some of the greatest quotes in the entire show.
Finn and Jake try to help a village of small people from a monster, who is actually Lumpy Space Princess (who Finn and Jake have been asked to bring home by her parents). Seriously lacking in any kind of mystery, interesting plot, character moments, or anything else, this is filler from beginning to end.
Ice King uses a freezing potion on Finn and Jake to force them to bond with them. This episode doesn't do anything out of character for Ice King, but I feel he's and little creepier here than usual. The set-up allows for some good laughs, but for the most part this one just feels slightly uncomfortable and tedious. It makes my legs itch.
Wizards of Ooo come together for a battle to the death (where no one dies) using only magic, with the special prize being a kiss from PB. To prevent Ice King from winning, Finn joins the fight. What a disappointment. The potential for this episode was so high, but the result was pretty boring. Not much happens here worth mentioning.
'Fionna And Cake'
An alternate version of Ooo wherein all the genders of the show's characters are reversed. While I enjoy the twist at the end, most of this episode just feels like low-grade storytelling, relying far more on the gimmick than on the actual events taking place. It all makes sense in the end, but the journey there is tedious. Not a fan of Fionna and Cake.
'What Was Missing'
People have their personal stuff stolen by a Door Lord, which leads Finn, Jake, Marceline, and PB to come together for a jam session in order to get their stuff back. It sounds a little lame, but it works really well. This is the first time we really see anything about Marceline and PB's past, a relationship filled with layers of mystery. A very sweet episode filled with memorable moments, but not quite as amazing as I think most people believe it to be.
Someone is stealing Tree Trunks' apples, Finn and Jake are on the case, and I'm already bored typing this. Beyond her trip to the crystal dimension and back, Tree Trunks is an uninteresting character and episodes focused on her are generally either boring or weird and bad. Skip it.
A mystery invitation to a masquerade dinner party puts Finn, Jake, PB, LSP, and other abbreviated names in a spooky house that seems to be haunted by spirits. A sort of sequel to the season 2 episode 'Mystery Train', this episode features some great tension, fun animation, several twists, and a bizarre and creepy loose plot thread that doesn't get resolved for several seasons. One of the better mystery/horror episodes.
'From Bad To Worse'
PB starts a zombie outbreak again, and it's up to Finn to use science to cure it. Another semi sequel (this one to the first episode of the show), this one uses the familiar set up to create an even more tense and hilarious episode than the original. It's always impressive seeing what this show can accomplish in just 11 minutes, and this one is just packed.